add acceptance test for admin locking an event.

spec/features/admin_lock_event_spec.rb

@@ -0,0 +1,27 @@
+require 'rails_helper'
+
+feature 'Event locking' do
+  background do
+    create :venue, title: 'Empire State Building'
+    create :event, title: 'Ruby Newbies'
+
+    page.driver.basic_authorize SECRETS.admin_username, SECRETS.admin_password
+  end
+
+  scenario 'Admin signs in and locks an event to prevent it from being modified' do
+    visit '/admin'
+    click_on 'Lock events'
+
+    within 'tr', text: 'Ruby Newbies' do
+      click_on 'Lock'
+    end
+
+    expect(page).to have_content('Locked event Ruby Newbies')
+    click_on 'Ruby Newbies'
+
+    expect(page).to have_content('This event is currently locked and cannot be edited.')
+    expect(page).to_not have_selector('a', text: 'edit')
+    expect(page).to_not have_selector('a', text: 'delete')
+  end
+end
+